Lost Patrol is a 2-player board game designed by Jake Thornton and produced by Games Workshop way back in the day when they still did other things than cranking out new editions and codices for Warhammer 40,000.
One player takes control of a group of Space Marine Scouts (the eponymous lost patrol) trapped on a jungle Death World. His goal is to find the Marines' dropship and get the fuck off that hellhole. The second player controls the "local fauna". His goal is to cackle maniacally while the Scouts drop like flies.
The game is played on a modular map consisting of hex tiles that is continually expanded as the Scouts move along. It is so ridiculously unbalanced that even finding the dropship is considered a major victory for the Marines. Consider Space Hulk: goddamn Terminators have a hard time against genestealers. According to Thornton himself, this is intentional and part of the fun. The only way to make Lost Patrol "fair" is to take turns at playing the marines and see who gets eaten faster.
Original copies of Lost Patrol are reasonably easy to find, but if for some reason you can't be bothered with tracking one down, you can easily simulate the experience of playing the Scout side by pulling a burlap sack over your head and having a buddy lock you into a small room filled with angry feral cats.
The 2016 Re-Release
After the game had languished in obscurity for a couple of years, GW announced a re-release in May 2016, albeit in the form of "a newly designed game" rather than a simple reprint. June 2016 was given as the shipping date.
September 2016 White Dwarf brought us additional rules for Space Marine Terminators, giving the SM player a slightly lower chance of losing.
Another White Dwarf made it easier again by having missile launchers that could wipe three 'stealers off the board in one shot and sniper rifles in the game.